1. Field of Invention
This invention relates to gauging tire pressure without connection to the tire interior, specifically using rotating permanent magnets and a display device that uses magneto-optical effects in liquid crystals or other materials to respond to magnetic field direction.
2. Description of Prior Art
Fluor Hanford, Inc. has developed a magnetically-coupled pressure readout based on Bourdon-tube principles. Bourdon-tube gauges are fragile, complex, and produce relatively weak forces. Accordingly, Bourdon tube mechanisms are not well suited for supporting appreciable magnet masses and for overcoming friction. In fact, forces generated by the interaction of the earth""s magnetic field with a supported magnet can exceed those available from Bourdon tube mechanisms. For readout, the Fluor Hanford device employs a conventional, horizontally oriented, gravity stabilized magnetic compass needle supported by a single-jewel suspension. Accordingly, the Bourdon tube mechanism is necessarily vertically oriented and this type of device is only suited for stationary applications. Additionally, the Flour Hanford device does not include a means for compensating for errors due to extraneous magnetic fields and does not include a means for extending the operating distance.
Angular coupling between rotating elements on shafts via magnetic fields is well known. For example, U.S. Pat. No. 5,382,792 to Hurst et al, describes a coupling mechanism wherein permanent magnet pairs are incorporated into coaxial shafts to provide an instantaneous indication of the orientation of a rotating shaft internal to a motor vehicle engine. Such coupling mechanisms employ multiple permanent magnets, oriented pole-face to pole-face. In these types of devices, magnetic coupling between the pole faces of paired permanent magnets aligns the xe2x80x9coutputxe2x80x9d shaft with the xe2x80x9cinputxe2x80x9d shaft. To be effective, such mechanisms require narrow gaps between the pole faces of the respective magnets. These types of devices are hermetically encapsulated for protection from environmental debris and require penetration of the engine wall.
U.S. Pat. No. 3,777,565 to Munier et al. describes a sealed water or fluid meter with continuously rotating permanent magnets driven by impellers on input shafts magnetically coupled to magnets on outputs hafts for inducing synchronized rotation. The rotation per unit time of the output shaft indicates the flow rate. Angular displacements (errors) between the xe2x80x9cinputxe2x80x9d and xe2x80x9coutputxe2x80x9d shafts are tolerated and even increase torque coupling from the input magnet to the output magnet.
Numerous devices include mechanisms moving a permanent magnet in response pressure or other force to induce a sensed effect in a material responsive to variation in magnetic field strength. For example, U.S. Pat. No. 4,006,402 to Mincuzzi, U.S. Pat. No. 4,843,886 to Koppers, et al, and U.S. Pat. No. 4,627,292 to Dekrone, each describe a device based on either magnetoresistance and magnetic saturation. U.S. Pat. No. 4,339,955 to Iwasaki describes a mechanism that exploits variation in the incremental permeability of a magnetically soft material. Devices based on the sensing the strength or flux of a magnetic field rather than field direction typically are very sensitive to changes in spacing, small misalignments, and extraneous magnetic fields. Accordingly, such devices generally require careful and extensive calibration before measurements are made.
U.S. Pat. No. 4,866,982 to Gault describes a tire pressure monitoring system where a stationary Hall-effect sensor measures spacing between a fixed magnet and a second magnet moveable in response to a linear pressure actuator. Changes in spacing between the magnets affect features of the combined magnetic field pattern. Variation in the combined pattern is determined from signal waveforms generated as the spaced magnets, rotating with a wheel, sweep by a stationary sensor. This device requires close coupling between magnet and sensor and penetration into the pressurized interior of the tire and rim.
U.S. Pat. No. 5,814,725 to Furuichi et al. describes a mechanism that penetrates a tire rim wherein a piston-driven screw rotates a permanent magnet. The strength of the magnetic field is detected by a stationary Hall-effect sensor that is mounted transversely to the magnet rotation axis. This type of device typically shares the same problems as the other devices that depend on sensing magnetic field strength.
U.S. Pat. No. 5,047,629 to Geist describes a hermetically sealed mechanism for sensing linear displacements of a ferromagnetic armature (e.g., a single turn in a coil spring) according to the attractive force on freely rotating magnet. Disadvantages inherent in this type of device relate to the small distances required between the armature and the magnet, to the small amount of rotational displacement of the magnet produced, and to inadvertent magnetization of the armature.
Other examples of remote pressure reporting mechanisms involve changes in electromagnetic induction or inductive coupling between active elements. For example, U.S. Pat. No. 5,455,508 to Takahashi utilizes a form of time-varying (alternating current) electrical excitation. Disadvantages of these types of devices relate to the need to provide a source of operating power within the pressure container and to inadvertent production of eddy currents in nearby conductive materials that will distort the desired field. These types of devices do not sense magnetic field direction.
Still other concepts of remote pressure sensing involve a change the state indicator responding a preset pressure level. For example, U.S. Pat. No. 3,946,175 to Sitabkhan describes switching a magnetically susceptible reed in response to pressure actuated displacement of a magnet. U.S. Pat. No. 5,542,293 to Tsuda et al. describes a conventional bellows actuated mechanism that uses a fixed and a moveable magnet to switch the orientation of a third magnet. U.S. Pat. No. 5,717,135 to Fioretta et al. describes use of magnetic coupling to switch the state of a transducer from producing to not producing a signal. These types of mechanisms are incapable of producing a continuous output responsive to pressure.
Other examples of remote monitoring of vehicle tire pressure involve wireless or telemetric transmission of data. For example, U.S. Pat. No. 5,960,804 to McClelland describes a radio transmitter that sends data collected and stored in a memory device within a tire to an external receiver. This active device requires a source of electrical energy (a battery) inside the tire. Alternatively, U.S. Pat. No. 6,053,038 to Schramm et al. proposes a scheme where an external oscillator circuit generates electromagnetic signals coupling to and energizing a second oscillator within the tire, which changes state responsive to tire pressure and/or other sensed parameters.
Several mechanisms besides Bourdon tubes have been proposed for converting pressure or force into rotary motion. For example, U.S. Pat. No. 4,307,928 to Petlock describes a helical bellows for imparting rotational displacement when compressed mechanically in order to make an improved electrical contact. A single, high pitch helical lead is employed because the desired rotational translation is small. U.S. Pat. No. 5,103,670 to Wu describes the use of a helical screw to convert linear displacement from a conventional bellows to actuate a directly viewed rotary dial or pointer. U.S. Pat. No. 6,082,170 to Lia et al. describes a blood pressure apparatus that uses a diaphragm bellows and a compressible helical ribbon spring to rotate a dial pointer. None of these types of device employs magnetic coupling for remote sensing.
U.S. Pat. No. 3,876,286 to Deutscher et al. describes orienting nematic liquid crystals in response to electric and magnetic fields and hence affecting light transmission in electrically controlled liquid crystal cells. U.S. Pat. No. 4,128,496 to Cole et al. describes various dichroic liquid crystal compositions for use in displays.
U.S. Pat. No. 5,412,500 to Fergason describes a method for continuously rotating the direction of linearly polarized light by a liquid crystal cell in response to an electrical input across the cell. This type of device employs quarter wave phase retardation means and a polarization analyzer to effect polarization rotation and requires monochromatic light. The degree of polarization rotation is controlled by the strength of the electrical field, which has a fixed direction.
U.S. Pat. No. 5,798,807 to Prehn proposes a multi-element device for projecting temporally modulated images. In this type of device the degree of polarization rotation is controlled by the strength of the electrical, magnetic, or mechanical impetus, not the orientation of the impetus.
U.S. Pat. No. 4,114,990 to Mash et al. describes a cell filled with a cholesteric (i.e., chiral nematic) liquid crystal for rotating the polarization of incident plane light in response to an electrical field applied transversely across the cell. A simulated pointer meter is to be produced by progressively varying the orientation of a polarizing layer over the cell. This type of device depends on controlling (by means of the electric field strength) the balance between homeotropic alignment of the liquid crystal at one inner cell surface and parallel homogeneous alignment at the other inner cell surface, which affects the degree of helical twist of the cholesteric liquid crystal.
U.S. Pat. No. 4,768,862 to McAdams describes a liquid crystal cell employing a uniform transverse magnetic field to switch the linear polarization orientation of an incident light beam in a wavelength selective fashion. In this type of devic, the orientation of the liquid crystal director is switched from twisted nematic to homeotropic by increasing the strength of the transverse magnetic field.
U.S. Pat. No. 4,214,819 to Pohl et al. proposes using a combination of electric and magnetic fields to increase the switching speed of an electro-optical liquid crystal cell and controlling the color of a display. This type of device uses predetermined electric and magnetic field directions and is controlled by varying the electric field strength.
The invented magnetically coupled gauge comprises a sender unit with a pressure sensor or other property transducer coupled for rotating a magnetic field source and a magneto-optical liquid crystal display unit responding to the direction of the magnetic field produced at a distance. In particular, the display unit exploits the magneto-optical effects of liquid crystals to indicate direction of the magnetic field provided by the sender unit.
The magneto-optical liquid crystal display unit preferably is a thin, flexible patch comprising a liquid crystal cell, and is positioned such that the field produced by the rotating magnet of the sender unit has a substantial component in the plane of the cell. Individual pixels comprising the display have predetermined light polarization properties different from one another. The display unit provides a continuous response indicating direction of a vector sum of the magnetic fields experienced by the display as a whole at any particular location and time, the primary component of which is always determined by the rotated magnetic field source of the sender unit.
A particular embodiment of invented magnetically coupled gauge is intended to visually display externally, an indication of pressure within vehicle tires and other pressure vessels and/or vacuum vessels quickly and cleanly, without any need for penetration into or breach of the pressure vessel.
Advantages
The primary advantage of invented gauge the relates both to the ease of precisely controlling and then sensing magnetic field direction with magneto-optical liquid crystals as opposed to sensing and parameterizing flux or strength of a magnetic field.
Other advantages of the invented magneto-optical liquid crystal pressure gauge is its simplicity robustness, and an almost universal utility for visually indicating pressure within both pressurized and evacuated vessels, including a pneumatic vehicle tires.
Still other advantages of the invented magneto-optical liquid crystal pressure gauge is that it is passive, and capable of providing an indication of pressure within a pneumatic tire or sealed vessel using ambient light.
A particular utility of the invented magneto-optical liquid crystal pressure gauge is that dangerously low pressure of motor vehicle tires, particularly the multiple axle, tire wheels of large trucks, can be easily determined by visual inspection, rather than measurement, substantially enhancing traffic safety.
Other aspects of the invented magneto-optical liquid crystal pressure gauge relate to economical, direct, non-contaminating pressure indications.
Still other aspects of the invented magneto-optical liquid crystal gauge are associated with a passive display accomplished by prior orientation of pixels of magneto-optical liquid crystal display for placement within an external magnetic field that changes direction responsive to pressure or other transduced property within a closed vessel.
Other features of the invented magneto-optical liquid crystal gauge is that the display responding to the magnetic field can be essentially independent of the wavelength of the light. On the other hand, the display can respond to magnetic field direction with changes in color.
Still other features of the invented magneto-optical liquid crystal gauge relate to mechanisms for precise control of liquid crystal display systems with a magnetic field.
Another related feature of the invented magneto-optical liquid crystal gauge relates to minimization magnetic flux or field strength effects on the liquid crystal display systems.
Still further objects and advantages will become apparent from a consideration of the ensuing description and accompanying drawings.